This invention relates to plastic articles which are essentially impermeable to gases, particularly to those articles with a plastic surface having an organic polymer layer and metal layer deposited thereon and to a method for preparing such articles.
In the manufacture of various articles, such as films for packaging oxygen sensitive materials including meats and dairy products and the boundary wall of a vacuum insulating container, from synthetic resinous materials, the resinous material is advantageously impermeable to atmospheric gases and other vapors. Unfortunately, most common organic polymers such as the polyolefins, e.g., polyethylene, polymers of the monovinylidene aromatics, e.g., polystyrene, and the like, are not sufficiently resistant by themselves to the transmission of atmospheric gases and other vapors to be useful in those applications requiring impermeable, resinous materials.
Accordingly, it has become a common practice to treat or coat such polymers with any of a variety of materials in order to make the polymers more resistant to the transmission of gases therethrough. For example, U.S. Pat. No. 3,459,591 discloses employing a barrier polymer such as a polymer of vinylidene or vinyl chloride to improve the impermeability of the resinous substrate. Alternatively, the permeability of the resinous material can be decreased using a metal coating. Unfortunately, the permeability of the resultant structures are relatively high thereby precluding their use in various high barrier applications such as vacuum insulating panels. Moreover, when metal layers of sufficient thickness to provide the required impermeability are employed, undesirably thick and rigid structures are often obtained. Normal flexure or crumpling of such thick, metal coated structures markedly reduces their barrier properties.
To improve the barrier properties of a plastic material using only a thin metal layer, U.S. Pat. No. 3,916,048 discloses depositing a metal layer on the surface of the plastic material and overcoating the metal layer using an aqueous colloidal dispersion of an organic polymer which is adherent to the metal layer. Unfortunately, due to the surface irregularities inherent in the manufacture of molded articles and surface dirt such as fingerprints, dust and the like, the metal coating on the support's surface exhibits substantial pinholes, holidays and the like. Due to said imperfections, a substantial proportion of the barriers prepared in the manner disclosed in U.S. Pat. No. 3,916,048 are not as impermeable to gases as desired for some applications. While an improved barrier may be prepared by cleaning the surface of the substrate prior to the metallization thereof, irregularities due to mold stresses in the substrate are still evident, thereby reducing the effectiveness of the plastic support as a barrier material.
Therefore, in view of the deficiencies of the prior art in the preparation of articles comprising an organic plastic, particularly those articles wherein the organic plastic has a cylindrical surface, it would be highly desirable to provide the surface of the plastic with improved impermeability using a thin metal coating having reduced amounts of pinholes, holidays and other imperfections.